Thank-you for all the responses. So much to consider.
First re the ventilation. The units are fitted on a bulkhead with plenty of airflow, no direct sun and the boat
is in Tasmania so heat should not be a problem at this time of year. But it is to keep an eye on. The fitting instructions require space "on each side" for air circulation but they are designed to be mounted direct to a vertical surface so the only space behind is the few mm allowed for inside the casing. We could add a spacer to increase ventilation but there is no indication that failures to date have been due to overheat. They are warm not hot when charging.
Having 2 arrays and 2 controllers has enabled a swap as suggested by Barra. It was a swap that confirmed failure of two of the three units.
Yes re the OCV at 64.9V is close to the controller max of 65V but the max power 327 watt is well within the 360 watt of the controller. Am I correct to say that when current is flowing voltage will never be close to OCV?
We have a Bogart Trimetric 2030 battery monitor. It is the discrepancy between its readout and the controllers that has increased our concern that the Powertech MP-3735 may not be reliable. The most recent replacement controller (the fifth unit) was only fitted three days ago so not much data yet to draw conclusions from. Our batteries are in good condition, we are not using much power at present and the controllers have moved to FLOAT each morning after only a few hours of solar input - just as expected.
However the Trimetric battery monitor display has shown input amps considerably higher than the combined totals showing on the 2 controllers and at other times the opposite - input amps much lower then the combined totals. These readings being when there is no other charging source and allowing for the minimal load (about 1.5A) when everything non essential is off.
These discrepancies, added to the 3 failed units have lead to our concern that the controllers are not the reliable, highly efficient MPPT controllers we want to match our efficient panels. GILow's comments reinforce these concerns.
GILow says "Maybe the multiple units are confusing one another in their attempts to multistage charge
. Maybe they are a dud batch from whichever manufacturer made them. But I do think you will go crazy trying to get that level of electronic equipment working satisfactorily. And even if you do get something working, how long do you really think it will last?" Grrrr! We've already had to replace 3 units.
This raises the possibility that the units lack the sophistication to work efficiently when two controllers are charging a single
battery bank. Barra says "The problem i have is the 2 controllers sense each others charging volts on the battery and one goes to float too soon" - is that what we can always expect with 2 controllers charging 1 bank or only with poor quality/ less sophisticated controllers?
What do we do now? Wait for another failure which might be outside the 12 month warranty or while on a passage
? I'd like to return these for refund so we can invest in better quality units. Unfortunately Jaycar don't carry any of the brand names mentioned - Outback, Morningstar, Victron.
This brings me back to my initial question - is there a way to show that the controllers do not meet their advertised performance standard "uses the latest MPPT technology at all times which gives the maximum available output of the solar module". Perhaps Jaycar will allow refund without such proof. At this point we are certainly glad we purchased from local supplier.
Thanks for suggested alternatives. I will take a closer look at the Victron 100/30. I thought that charging profiles on the Victron could only be done by selecting one of the programmed options rather than entering bulk and float separately. Not so says Mitiempo. And does it have a display? It would seem a retrograde step to have only limited option dip switches and no display on the units.